Sadly, my Voyager Anniversary (vintage 1992) "decomposed", a know issue with some batches of unstable celluloid used to make this pen. I managed to mix/match and solvent weld a working Frankenpen, except for the clip, which was oxidized by the decomposing celluloid and broke (another relatively common issue with the cap design of that era).
Visconti, unfortunately, flatly refused to sell me a spring (despite the fact that the problem was caused by a material defect). I was reluctant to send them the pen, unsure of what I might get back, so I decided to make my own new clip spring from stainless piano wire that should be immune to oxidation.
Here's the rough shaping of the clip spring. It is the same as the flap band spring used by Visconti.
This illustrates where the spring must fit. The spring is held and tensioned by an inner cap that has a slot cut into it to accomodate the thickness of the spring. Once inserted, the junction between the clip and spring is under considerable tension, so the attachment must be strong and durable. I considered silver soldering, but settled on high quality epoxy.
This shows the finished repair after the epoxy cured for several days and the spring was tensioned and fixed with the inner cap.. The bonus is that the clip tension is much improved over the original design, which would not stabilize the pen in a shirt pocket. It has been more than two months with no sign of "pull out" or failure, so I think it is stable and the smooth contour of the dark grey epoxy looks kind of attractive.